Electronic throttle control ETC has been applied to automotive vehicles in which an electrical actuator, driven by an electrical signal from a controller, positions an engine inlet air or throttle valve. When applied in an air-lead engine control system in which engine fueling is controlled in response to inlet air rate, ETC provides a platform on which a variety of control benefits become available.
In typical conventional ETC systems, an accelerator pedal position sensor communicates an operator commanded engine operating point to a controller. The controller in turn determines a desired throttle position and issues a digital command appropriate to drive the throttle valve position toward the desired throttle valve position in accord with an applied control function. The issued command is used to drive an actuator, such as a motor, which rotates with the throttle valve.
Accordingly, ETC provides a mapping between sensed accelerator pedal motion and desired throttle valve motion. Such mapping is known not to be fixed. For example, conventionally known inputs attributed to vehicle cruise control, idle speed control, traction control, and engine torque management may override such mapping temporarily, driving throttle valve position away from a position corresponding to sensed accelerator pedal position. Furthermore, as described in U.S. Pat. No. 4,597,049, the gain applied between accelerator pedal motion and throttle valve motion may be made variable for improved performance and controllability.
Further advantages in vehicle control, driveability, and performance are available through variable mapping than are provided for in the prior art. It may be desirable under certain driving conditions to limit throttle authority, or to redefine ETC control resolution. For example, it may be desirable at low vehicle speeds to restrict the maximum achievable throttle valve opening to constrain vehicle motion, improving vehicle controllability and smoothness at tip-in. Such constraints may become less attractive as vehicle speed increases. Furthermore, at low vehicle speeds, controllability of the vehicle may be improved by varying the mapping between accelerator pedal motion and throttle valve motion in a manner that requires an increased amount of pedal motion for a fixed amount of valve motion, improving control resolution so the vehicle operator may achieve precisely a desired throttle valve opening. At intermediate vehicle speeds, the high degree of control resolution may be relaxed slightly, so the operator need not impart a substantial amount of pedal motion to significantly move the throttle valve. Finally, at high vehicle speeds, vehicle response may be improved by a low degree of control resolution, wherein little pedal motion may result in significant throttle valve motion.